Synthesis of Zeolites: An Overview

Abstract

Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents and catalysts. Zeolite synthesized from CFA is a minor but interesting product, with high environmental applications. Zeolites may be easily obtained from CFA by relatively cheap and fast conversion processes. This paper provides an overview on the methodologies for zeolite synthesis from CFA, and a detailed description of conventional alkaline conversion processes, with special emphasis on the experimental conditions to obtain high cation exchange capacity (CEC) zeolites. Zeolitic products having up to 3 meq g−1 may be easily obtained from high-glass CFA by direct conversion. A review of potential applications of different zeolitic products for waste water and flue gas treatment is also given. The examination of the data presented by different authors reveals that one of the main potential application of this material is the uptake of heavy metals from polluted waste waters. The zeolitic material may be also used for the uptake of ammonium from polluted waters but high concentrations of other cations may considerably reduce the ammonium absorption efficiencies due to ion competition. Some of the zeolites synthesized may be also used as molecular sieves to adsorb water molecules from gas streams or to trap SO2 and NH3 from low-water gaseous emissions Keywords: cation exchange capacity, coal fly ash, molecular sieves, heavy metals and ammonium uptake, zeolite synthesis